Method for depositing silicon oxide film having improved quality by peald using bis(diethylamino)silane

ABSTRACT

In a method of depositing a silicon oxide film using bis(diethylamino)silane (BDEAS) on a substrate in a reaction space by plasma-enhanced atomic layer deposition (PEALD), each repeating deposition cycle of PEALD includes steps of: (i) adsorbing BDEAS on the substrate placed on a susceptor having a temperature of higher than 400° C. in an atmosphere substantially suppressing thermal decomposition of BDEAS in the reaction space; and (ii) exposing the substrate on which BDEAS is adsorbed to an oxygen plasma in the atmosphere in the reaction space, thereby depositing a monolayer or sublayer of silicon oxide.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation and claims priority to U.S. Pat. Application Serial No. 16/999,065 filed Aug. 21, 2020 titled METHOD FOR DEPOSITING SILICON OXIDE FILM HAVING IMPROVED QUALITY BY PEALD USING BIS-DIETHYLAMINO)SALINE, which claims the benefit of U.S. Provisional Pat. Application No. 62/891,160 filed Aug. 23, 2019 titled METHOD FOR DEPOSITING SILICON OXIDE FILM HAVING IMPROVED QUALITY BY PEALD USING BIS-DIETHYLAMINO)SALINE, the disclosures of which are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention generally relates to a method for depositing a silicon oxide film having improved quality (e.g., excellent chemical resistance such as low wet etching rate, particularly at sidewalls and bottom of a trench) by plasma-enhanced atomic layer deposition (PEALD) using bis(diethylamino)silane (BDEAS).

Description of the Related Art

As a method of depositing a silicon oxide film by PEALD, a deposition method using BDEAS and oxygen plasma is known. However, when depositing a silicon oxide film in a trench formed in a substrate using the conventional method, film quality (chemical resistance such as low dry or wet etching rate, leakage current, shrinkage, in-plane uniformity, etc.) at sidewalls and bottom of the trench tends to be insufficient or unsatisfactory as compared with film quality on a top surface of the substrate. In general, by increasing RF power and/or duration of an RF power pulse, film quality is expected to be improved. However, when the trench has a high aspect ratio (e.g., 3 or higher, particularly 10 or higher), sufficient improvement of film quality has not been achieved, particularly at film quality at sidewalls and bottom of the trench, due to directionality or the anisotropic nature of plasma (e.g., ion bombardment by direct plasma composed of ions).

In view of the conventional technology, an embodiment of the present invention provides a method for depositing a silicon oxide film having improved quality by PEALD using BDEAS.

Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made.

SUMMARY OF THE INVENTION

As discussed above, as process parameters, increasing RF power and/or duration of an RF power pulse may not be sufficient or effective to improve film quality at sidewalls and bottom of a trench in depositing a silicon oxide film by PEALD using BDEAS due to the anisotropic nature of plasma. Thus, as a process parameter, increasing a deposition temperature can be considered to be a good candidate. However, a skilled artisan in the art is likely to consider that BDEAS starts thermal decomposition at a temperature higher than 400° C., and thus, in order to obtain a high-quality silicon oxide film using BDEAS, the process temperature in PEALD should preferably be 400° C. or lower. For example, U.S. Pat. No. 8,227,032 states that high quality films, with very low carbon and hydrogen contents, are preferably deposited between 200 and 400° C. If BDEAS is thermally decomposed, amines, oxides of carbon, oxides of nitrogen, and oxides of silicon are produced as thermal decomposition products, resulting in deposition of a silicon oxide film having relatively high contents of carbon, nitrogen, and hydrogen. Further, for example, WO2016/954531 states that the wafer surface is heated to a temperature in the range of about 450° C. to about 650° C., so that the absorbed silicon precursor thermally decomposes on the wafer surface to form a monolayer or sub-monolayer silicon film. As discussed above, a skilled artisan is fairly likely to expect BDEAS also to be thermally decomposed at a temperature higher than 400° C. It should be noted that, unlike typical PEALD where an adsorbed silicon precursor containing carbon/nitrogen reacts with an oxygen plasma and forms a silicon oxide film by displacement reaction displacing carbon/nitrogen by oxygen, in WO2016/954531, first, the absorbed silicon precursor thermally decomposes on the wafer surface to form a monolayer or sub-monolayer silicon film, and then is exposed to a source of oxygen, thereby oxidizing the silicon film to form a SiO₂ film.

Contrary to the skilled artisan’s expectation, the present inventors have discovered that BDEAS is stable and is not significantly decomposed at a temperature of higher than 400° C. but no higher than 650° C., and by using such a high temperature as a deposition temperature by PEALD, film quality of a deposited silicon oxide film can be significantly improved, particularly, at sidewalls and bottom of a trench. In some embodiments, in a method of depositing a silicon oxide film using BDEAS on a substrate in a reaction space by PEALD, each repeating deposition cycle of PEALD comprises steps of: (i) adsorbing BDEAS on the substrate placed on a susceptor having a temperature of higher than 400° C. in an atmosphere substantially suppressing thermal decomposition of BDEAS in the reaction space; and (ii) exposing the substrate on which BDEAS is adsorbed to an oxygen plasma in the atmosphere in the reaction space, thereby depositing a monolayer of silicon oxide.

In some embodiments, the temperature of the susceptor is lower than 650° C. In some embodiments, the atmosphere has a pressure of 1,000 Pa or less and an oxygen concentration of 5% to 70%. Further, in some embodiments, the atmosphere has a pressure of 400 Pa or less. Still in some embodiments, the atmosphere has an oxygen concentration of 30% to 60%.

For purposes of summarizing aspects of the invention and the advantages achieved over the related art, certain objects and advantages of the invention are described in this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

Further aspects, features and advantages of this invention will become apparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

These and other features of this invention will now be described with reference to the drawings of preferred embodiments which are intended to illustrate and not to limit the invention. The drawings are greatly simplified for illustrative purposes and are not necessarily to scale.

FIG. 1A is a schematic representation of a PEALD (plasma-enhanced atomic layer deposition) apparatus for depositing a silicon oxide film, usable in an embodiment of the present invention.

FIG. 1B illustrates a schematic representation of a precursor supply system using a flow-pass system (FPS) usable in an embodiment of the present invention.

FIG. 2 shows a schematic process sequence of PEALD in one according to an embodiment of the present invention wherein a cell in gray represents an ON state whereas a cell in white represents an OFF state, and the width of each column does not represent duration of each process.

FIG. 3 shows a graph indicating the schematic relationship between film thickness and susceptor temperature in Reference Example 1.

FIG. 4 is a chart showing STEM photographs of cross-sectional views of trenches subjected to deposition of silicon oxide films at different temperatures (“As depo”), followed by wet etching (“After DHF dip”).

FIG. 5 is a chart showing STEM photographs of cross-sectional views of trenches subj ected to deposition of silicon oxide films at different pressures, different oxygen concentration, and different durations of purging (“As depo”), followed by wet etching (“After DHF dip”).

FIG. 6 is a chart showing the deposition conditions used in deposition shown in FIG. 4 , and film properties of resultant silicon oxide films, including color versions of images of thin-film thickness profile measurement by 2D color map analysis of the films.

FIG. 7 is a schematic graph showing the relationship between wet etching rate and plasma bombardment on a surface according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In this disclosure, “gas” may include vaporized solid and/or liquid and may be constituted by a single gas or a mixture of gases, depending on the context. Likewise, an article “a” or “an” refers to a species or a genus including multiple species, depending on the context. In this disclosure, a process gas introduced to a reaction chamber through a showerhead may be comprised of, consist essentially of, or consist of an aminosilane precursor and an additive gas. The precursor may contain only bis(diethylamino)silane (BDEAS) or contain BDEAS as a primary precursor and one or more secondary precursor(s) which is/are either aminosilane or non-aminosilane to the extent not interfering with plasma oxidation of BDEAS to form silicon oxide. The additive gas may include a plasma-generating gas for exciting the precursor to deposit silicon oxide when RF power is applied to the additive gas. The additive gas may contain a reactant gas for oxidizing the precursor and may further contain an inert gas which may be fed to a reaction chamber as a carrier gas and/or a dilution gas to the extent not interfering with plasma oxidation forming silicon oxide. The precursor and the additive gas can be introduced as a mixed gas or separately to a reaction space. The precursor can be introduced with a carrier gas such as a rare gas. A gas other than the process gas, i.e., a gas introduced without passing through the showerhead, may be used for, e.g., sealing the reaction space, which includes a seal gas such as a rare gas. In some embodiments, the term “precursor” refers generally to a compound that participates in the chemical reaction that produces another compound, and particularly to a compound that constitutes a film matrix or a main skeleton of a film, whereas the term “reactant” refers to a compound, other than precursors, that activates a precursor, modifies a precursor, or catalyzes a reaction of a precursor, wherein the reactant may provide an element (such as O) to a film matrix and become a part of the film matrix, when RF power is applied. The term “inert gas” refers to a plasma-generating gas that excites a precursor when RF power is applied, but unlike a reactant, it does not become a part of a film matrix.

In some embodiments, “a monolayer” refers to a layer one molecule thick, and “a sublayer” refers to a subunit of layer which is not necessarily a monolayer but is a layer deposited in one cycle of ALD as a subunit part of a final film. In some embodiments, “film” refers to a layer continuously extending in a direction perpendicular to a thickness direction substantially without pinholes to cover an entire target or concerned surface, or simply a layer covering a target or concerned surface. In some embodiments, “layer” refers to a structure having a certain thickness formed on a surface or a synonym of film or a non-film structure. A film or layer may be constituted by a discrete single film or layer having certain characteristics or multiple films or layers, and a boundary between adjacent films or layers may or may not be clear and may be established based on physical, chemical, and/or any other characteristics, formation processes or sequence, and/or functions or purposes of the adjacent films or layers. Further, in this disclosure, any two numbers of a variable can constitute a workable range of the variable as the workable range can be determined based on routine work, and any ranges indicated may include or exclude the endpoints. Additionally, any values of variables indicated (regardless of whether they are indicated with “about” or not) may refer to precise values or approximate values and include equivalents, and may refer to average, median, representative, majority, etc. in some embodiments. Further, in this disclosure, the terms “constituted by” and “having” refer independently to “typically or broadly comprising”, “comprising”, “consisting essentially of”, or “consisting of” in some embodiments. In this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments.

In this disclosure, “continuously” refers to without breaking a vacuum, without interruption as a timeline, without any material intervening step, without changing treatment conditions, immediately thereafter, as a next step, or without an intervening discrete physical or chemical structure between two structures other than the two structures in some embodiments.

In this disclosure, a “step” or “recess” refers to any structure having a top surface, a sidewall, and a bottom surface formed on a substrate, which may continuously be arranged in series in a height direction or may be a single step, and which may constitute a trench, a via hole, or other recesses. Further, in this disclosure, a trench is any recess pattern including a hole/via and which has, in some embodiments, a width of 10 to 50 nm (typically 15 to 30 nm) (wherein when the trench has a length substantially the same as the width, it is referred to as a hole/via, and a diameter thereof is 10 to 50 nm), a depth of 30 to 200 nm (typically 50 to 150 nm), and an aspect ratio of 3 to 20 (typically 3 to 10).

In this disclosure, a SiO film includes not only SiO films, but also SiOC films, SiON films, SiOCN films, or the like, depending on the process recipe, wherein the film names are abbreviations indicating merely the film types (indicated simply by primary constituent elements) in a non-stoichiometric manner unless described otherwise.

FIG. 2 shows a schematic process sequence of PEALD in one according to an embodiment of the present invention wherein a cell in gray represents an ON state whereas a cell in white represents an OFF state, and the width of each column does not represent duration of each process. A first step (“Feed”) comprises feeding BDEAS to a reaction space in a pulse and adsorbing BDEAS on a substrate placed on a susceptor having a temperature of higher than 400° C. (preferably higher than 500° C. but not higher than 650° C.) in an atmosphere substantially suppressing thermal decomposition of BDEAS in the reaction space. In general, the higher the temperature, the more the improvement of film quality of a resultant silicon oxide film, particularly at sidewalls and bottom of the trench, can be expected as long as thermal decomposition of BDEAS can sufficiently or substantially be suppressed in the atmosphere. Preferably, the atmosphere has a pressure of 1,000 Pa or less (more preferably 400 Pa or less, e.g., 333 Pa to 400 Pa) and an oxygen concentration of 5% to 70% (more preferably an oxygen concentration of 30% to 60%) so that even when the deposition temperature is high, thermal decomposition of BDEAS can be suppressed. In some embodiments, oxygen as an oxidizer is fed to the reaction space at a flow rate of 400 sccm to 5600 sccm (preferably 1600 sccm to 4000 sccm) with one or more inert gas (e.g., rare gas such as Ar and/or He) fed at a flow rate of 400 sccm to 5600 sccm (preferably 2000 sccm to 4400 sccm). As an oxidizer, nitrogen dioxide can also be used. In this embodiment, the oxidizer is fed continuously throughout the deposition cycle. In the “Feed” step, BDEAS is fed using a flow of carrier gas which is an inert gas such as rare gas (e.g. Ar and/or He) fed at a flow rate of 2000 sccm. Since ALD is a self-limiting adsorption reaction process, the amount of deposited precursor molecules is determined by the number of reactive surface sites and is independent of the precursor exposure after saturation, and a supply of the precursor is such that the reactive surface sites are saturated thereby per cycle (“chemisorption” refers to chemical saturation adsorption). In this embodiment, the carrier gas is fed continuously throughout the deposition cycle.

The continuous flow of the carrier gas can be accomplished using a flow-pass system (FPS) wherein a carrier gas line is provided with a detour line having a precursor reservoir (bottle), and the main line and the detour line are switched, wherein when only a carrier gas is intended to be fed to a reaction chamber, the detour line is closed, whereas when both the carrier gas and a precursor gas are intended to be fed to the reaction chamber, the main line is closed and the carrier gas flows through the detour line and flows out from the bottle together with the precursor gas. In this way, the carrier gas can continuously flow into the reaction chamber and can carry the precursor gas in pulses by switching between the main line and the detour line. FIG. 1B illustrates a precursor supply system using a flow-pass system (FPS) according to an embodiment of the present invention (black valves indicate that the valves are closed). As shown in (a) in FIG. 1B, when feeding a precursor to a reaction chamber (not shown), first, a carrier gas such as Ar (or He) flows through a gas line with valves b and c, and then enters a bottle (reservoir) 20. The carrier gas flows out from the bottle 20 while carrying a precursor gas in an amount corresponding to a vapor pressure inside the bottle 20 and flows through a gas line with valves f and e, and is then fed to the reaction chamber together with the precursor. In the above, valves a and d are closed. When feeding only the carrier gas (noble gas) to the reaction chamber, as shown in (b) in FIG. 1B, the carrier gas flows through the gas line with the valve a while bypassing the bottle 20. In the above, valves b, c, d, e, and f are closed.

In some embodiments, the duration of “Feed” is 0.1 seconds to 3.0 seconds (preferably 0.2 seconds to 0.5 seconds).

Next, in the second step (“Purge-1”), the reaction space is purged so as to remove excess BDEAS and non-adsorbed BDEAS from the surface of the substrate. The purging can be accomplished simply by continuous flows of oxidizer and carrier gas which function as a purging gas, although a separate purging gas can be used. In some embodiments, the duration of purge is 0.2 seconds to 2.0 seconds (preferably 0.3 seconds to 1.0 seconds). In some embodiments, in PEALD, by shortening a duration of purge (e.g., to a range of 0.1 seconds to 0.5 seconds), some non-adsorbed BDEAS may remain on the top surface and in the trench, and this may result in lowering film quality on the top surface and at the bottom of the trench, while improving film quality on the sidewalls to a certain degree. This may be because a shorter duration of purge leaves more BDEAS in the trench which may stay in the trench like cloud which may partially block plasma from reaching the bottom, while more plasma energy reaches the sidewalls.

Next, in the third step (“RF Pulse”), BDEAS adsorbed on the substrate surface is exposed to an oxygen plasma, thereby depositing a monolayer or sublayer of silicon oxide on the substrate. In some embodiments, the period of RF power application (the period of being exposed to a plasma) is in a range of 0.2 seconds to 2.0 seconds (preferably 0.2 seconds to 1.2 seconds). The plasma exposure time can also be adjusted by changing the distance between upper and lower electrodes when conductively coupled parallel electrodes are used wherein by increasing the distance, the retention time in which the precursor is retained in the reaction space between the upper and lower electrodes can be prolonged when the flow rate of precursor entering into the reaction space is constant. In some embodiments, the distance (mm) between the upper and lower electrodes is 7.5 mm to 13 mm (preferably 7.5 mm to 10 mm). In some embodiments, RF power (W) (e.g., 13.56 MHz) for deposition is 50 W to 1000 W (preferably 200 W to 500 W) as measured for a 300-mm wafer which can be converted to units of W/cm² for different sizes of wafers.

After the third step, in the fourth step (“Purge-2”), the reaction space is purged so as to remove unreacted BDEAS and reaction by-products from the surface of the substrate. The purging can be accomplished simply by continuous flows of oxidizer and carrier gas which function as a purging gas, although a separate purging gas can be used. In some embodiments, the duration of purge is 0.1 seconds to 1.0 seconds (preferably 0.1 seconds to 0.3 seconds).

The process cycle can be performed using any suitable apparatus including an apparatus illustrated in FIG. 1A, for example. FIG. 1A is a schematic view of a PEALD apparatus, desirably in conjunction with controls programmed to conduct the sequences described below, usable in some embodiments of the present invention. In this figure, by providing a pair of electrically conductive flat-plate electrodes 4, 2 in parallel and facing each other in the interior 11 (reaction zone) of a reaction chamber 3, applying HRF power (13.56 MHz or 27 MHz) 25 to one side, and electrically grounding the other side 12, a plasma is excited between the electrodes. A temperature regulator is provided in a lower stage 2 (the lower electrode), and a temperature of a substrate 1 placed thereon is kept constant at a given temperature. The upper electrode 4 serves as a shower plate as well, and reactant gas and/or dilution gas, if any, and precursor gas are introduced into the reaction chamber 3 through a gas line 21 and a gas line 22, respectively, and through the shower plate 4. Additionally, in the reaction chamber 3, a circular duct 13 with an exhaust line 7 is provided, through which gas in the interior 11 of the reaction chamber 3 is exhausted. Additionally, a transfer chamber 5 disposed below the reaction chamber 3 is provided with a seal gas line 24 to introduce seal gas into the interior 11 of the reaction chamber 3 via the interior 16 (transfer zone) of the transfer chamber 5 wherein a separation plate 14 for separating the reaction zone and the transfer zone is provided (a gate valve through which a wafer is transferred into or from the transfer chamber 5 is omitted from this figure). The transfer chamber is also provided with an exhaust line 6. In some embodiments, the deposition of multi-element film and surface treatment are performed in the same reaction space, so that all the steps can continuously be conducted without exposing the substrate to air or other oxygen-containing atmosphere.

In some embodiments, in the apparatus depicted in FIG. 1A, the system of switching flow of an inactive gas and flow of a precursor gas illustrated in FIG. 1B (described earlier) can be used to introduce the precursor gas in pulses without substantially fluctuating pressure of the reaction chamber.

A skilled artisan will appreciate that the apparatus includes one or more controller(s) (not shown) programmed or otherwise configured to cause the deposition and reactor cleaning processes described elsewhere herein to be conducted. The controller(s) are communicated with the various power sources, heating systems, pumps, robotics and gas flow controllers, or valves of the reactor, as will be appreciated by the skilled artisan.

In some embodiments, a dual chamber reactor (two sections or compartments for processing wafers disposed close to each other) can be used, wherein a reactant gas and a noble gas can be supplied through a shared line whereas a precursor gas is supplied through unshared lines.

The film having filling capability can be applied to various semiconductor devices including, but not limited to, cell isolation in 3D cross point memory devices, self-aligned Via, dummy gate (replacement of current poly Si), reverse tone patterning, PC RAM isolation, cut hard mask, and DRAM storage node contact (SNC) isolation.

EXAMPLES

In the following examples where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. A skilled artisan will appreciate that the apparatus used in the examples included one or more controller(s) (not shown) programmed or otherwise configured to cause the deposition and reactor cleaning processes described elsewhere herein to be conducted. The controller(s) were communicated with the various power sources, heating systems, pumps, robotics and gas flow controllers or valves of the reactor, as will be appreciated by the skilled artisan.

Reference Example 1 (Thermal Stability of BDEAS)

In Reference Example 1, in order to examine thermal stability of BDEAS, a Si substrate on which a native or natural oxide film having a thickness of 1.20 nm was formed was placed in the apparatus illustrated in FIG. 1A with a gas supply system (FPS) illustrated in FIG. 1B. The atmosphere of the reaction chamber was controlled by feeding thereto BDEAS at 2000 sccm and oxygen at 2000 sccm under a pressure of 400 Pa without applying RF power to the reaction chamber, wherein a susceptor temperature was set in a range of 400° C. to 650° C. 800 seconds after the susceptor temperature reached the set temperature, the thickness of the film was measured at each set temperature. As a comparative reference example, the thickness of film was measured at each set temperature in the same manner as in Reference Example 1 except that no BDEAS was fed to the reaction chamber.

FIG. 3 shows a graph indicating the schematic relationship between film thickness and susceptor temperature. As shown in FIG. 3 , the thickness of the film with the BDEAS feed (“w/ Feed”) and the thickness of the film without the BDEAS feed (“w/o Feed”) were substantially the same in the entire temperature range. It should be noted that the thickness of the film appeared to increase as the temperature became higher even when no BDEAS was fed, and this is because the substrate itself (with the underlying natural oxide film) was further oxidized by oxygen, increasing the apparent thickness. Further, the film thickness was slightly greater when BDEAS was fed than when no BDEAS was fed at temperatures of 550° C., 600° C., and 650° C. This is because BDEAS was adsorbed on the substrate surface by heat. If BDEAS had been thermally decomposed at the set temperature, decomposed components (such as amine, oxide of carbon, oxide of nitrogen, and oxide of silicon) would have been continuously accumulated on the substrate surface, significantly increasing the film thickness particularly at higher temperatures. Thus, the result shown in FIG. 3 confirms that BDEAS is not thermally decomposed in a temperature range of 400° C. to 650° C.

Example 1 (Improvement of Film Quality at High Deposition Temperatures)

A silicon oxide film was deposited on a Si substrate (having a diameter of 300 mm and a thickness of 0.7 mm) having trenches with an opening of approximately 30 nm, which had a depth of approximately 90 nm (an aspect ratio was approximately 3), by PEALD process in order to determine film quality of the film, under the conditions shown in Table 1 below (varying the deposition temperature) in the process sequence illustrated in FIG. 2 using the apparatus illustrated in FIG. 1A and a gas supply system (FPS) illustrated in FIG. 1B. After deposition of silicon oxide film was complete, a cross-sectional view of each substrate with the trenches was photographed using STEM.

TABLE 1 Numbers are Approximate Temp. setting SUS temp (°C). See FIG. 4 Depo Pressure (Pa) 400 Electrode Gap (mm) 7.5 Feed time (s) 0.2 Purge-1 (s) 0.3 RF time (s) 1 Purge-2 (s) 0.1 RF power (W) 500 Precursor BDEAS Carrier Ar Carrier flow (slm) 2.0 Dilution Ar (slm) 2.0 Seal He (slm) 0.2 O2 (slm) 4.0 Number of cycles 500

After completion of deposition of each silicon oxide film (having an average film thickness of 25 nm on the top surface), the substrate was subjected to wet etching (by dipping the substrate in a solution of dHF having a concentration of 1% for 30 seconds at 22° C.). Further, after wet etching, a cross-sectional view of each substrate with the trenches was photographed using STEM.

FIG. 4 is a chart showing STEM photographs of cross-sectional views of trenches subjected to deposition of silicon oxide films at different temperatures (“As depo”), followed by wet etching (“After DHF dip”). In FIG. 4 , “Side/Top [%]” refers to a ratio [%] of thickness of the sidewall portion when deposited to that of the top portion, and “WERR [TOX ratio]” refers to wet etching rate of each portion relative to that of standard thermal oxide film. As shown in FIG. 4 , when the deposition temperature was 400° C. or higher, particularly higher than 500° C. (more preferably 550° C. or higher), the film quality of the sidewall portion was improved.

Example 2 (Improvement of Film Quality With Other Parameters)

silicon oxide film was deposited on a Si substrate in the same manner as in Example 1 except the conditions shown in Table 2 below.

TABLE 2 Numbers are Approximate UHT-6 UHT-7 UHT-8 UHT-9 UHT-10 UHT-11 Temp. setting SUS temp (°C). 650 Depo Pressure (Pa) 400 400 1000 3000 400 400 Purge-1 (s) 0.3 2 2 2 0.3 0.3 Carrier Ar (slm) 2.0 2.0 2.0 2.0 2.0 0.4 Dilution Ar (slm) 2.0 2.0 2.0 2.0 5.6 2.0 O2 (slm) 4.0 4.0 4.0 4.0 0.4 5.6 O2/(O2+Ar) (%) 50 50 50 50 5 70

After completion of deposition of each silicon oxide film, the substrate was subjected to wet etching in the same manner as in Example 1. Further, after wet etching, a cross-sectional view of each substrate with the trenches was photographed using STEM. It should be noted that when the deposition pressure was 3,000 Pa in UHT-9, film deposition became highly abnormal and thus, wet etch evaluation of this sample was not conducted.

FIG. 5 is a chart showing STEM photographs of cross-sectional views of the trenches subjected to deposition of the silicon oxide films at different pressures, different oxygen concentration, and different durations of purging (“As depo”), followed by wet-etching (“After DHF dip”). In FIG. 5 , “Side/Top [%]” and “WERR [TOX ratio]” denote the same meanings as in FIG. 4 . As shown in FIG. 5 , at a high deposition temperature (650° C.), when the deposition pressure was 400 Pa in UHT-7, as compared with in UHT-8 (1,000 Pa), the film quality of the sidewall portion was improved. However, the film quality of the top portion was not improved at a pressure of 400 Pa in UHT-7, as compared with in UHT-8 (1,000 Pa), and the film quality of the bottom portion was worsened at a pressure of 400 Pa in UHT-7, as compared with in UHT-8 (1,000 Pa). This may be because plasma bombardment received by a surface of each portion would be in the order of Top (400 Pa) > Top (1000 Pa) > Bottom (400 Pa) > Bottom (1000 Pa) > Side (400 Pa) > Side (1000 Pa), and there would be optimal plasma bombardment for improving film quality around at Bottom (1000 Pa), and when plasma bombardment is higher or lower than the optimal plasma bombardment, film quality would be less improved as schematically illustrated in FIG. 7 . A plasma is a partially ionized gas with high free electron content (about 50%), and when a plasma is excited by applying AC voltage between parallel electrodes, ions are accelerated by a self dc bias (V_(DC)) developed between plasma sheath and the lower electrode and bombard a film on a substrate placed on the lower electrode in a direction perpendicular to the film (the ion incident direction). Based on this non-limiting theory, a skilled artisan would be able to adjust film quality of each portion as desired by manipulating the deposition pressure (by doing this, film quality of the bottom portion and that of the sidewall portion (and further that of the top portion) can be adjusted at substantially the same degree). The bombardment of a plasma can be represented by plasma density (quantity of plasma active species) or kinetic energy of ions, and plasma density can be evaluated as disclosed in U.S. Pat. Publication No. 2017/0250068, the disclosure of which is herein incorporated by reference in its entirety.

Also as shown in FIG. 5 , at a high deposition temperature (650° C.), when a concentration of oxygen in the oxidizer gas (oxygen plus argon in this embodiment) was 50% in UHT-6, as compared with in UHT-10 (5%) and UHT-11 (70%), the film quality of the sidewall portion was improved. However, the film quality of the top portion was worsened at a concentration of oxygen of 50% in UHT-6, as compared with in UHT-10 (5%) and UHT-11 (70%). This may be because not only an oxygen plasma but also an argon plasma contributes to film quality of the sidewall portion, and when a ratio of an oxygen concentration and an argon concentration is approximately equal (e.g., ±10%, i.e., 40% to 60%), film quality of the sidewall portion can significantly be improved. Based on this non-limiting theory, a skilled artisan would be able to adjust film quality of each portion as desired by manipulating the oxygen concentration.

Further, as shown in FIG. 5 , at a high deposition temperature (650° C.), when a duration of purge was 0.3 seconds in UHT-6, as compared with in UHT-7 (2.0 seconds), the film quality of the sidewall portion was improved. However, the film quality of the top portion and that of the bottom portion were worsened at a duration of purge of 0.3 seconds in UHT-6, as compared with in UHT-7 (2.0 seconds). This may be because some non-adsorbed BDEAS may remain on the top surface and in the trench in a duration of purge of 0.3 seconds, and this may result in lowering film quality of the top portion and that of the bottom portion, while improving film quality of the sidewall portion to a certain degree. This may be because a shorter duration of purge leaves more BDEAS in the trench which may stay in the trench like cloud which may partially block plasma from reaching the bottom, while more plasma energy reaches the sidewalls. Based on this non-limiting theory, a skilled artisan would be able to adjust film quality of each portion as desired by manipulating the oxygen concentration.

Example 3 (Improvement of Film Quality - Blanket Deposition)

A silicon oxide film was deposited on a Si substrate without trenches in the same manner as in Example 1 except this was blanket deposition (not pattern deposition).

After completion of deposition of each silicon oxide film, the substrate was subjected to wet etching in the same manner as in Example 1. Further, after wet etching, film properties of each silicon oxide film were evaluated in terms of average thickness, in-plane thickness uniformity, and wet etching rate.

FIG. 6 is a chart showing the deposition conditions used in deposition shown in FIG. 4 , and film properties of the resultant silicon oxide films, including color versions of images of thin-film thickness profile measurement by 2D color map analysis of the films. In FIG. 6 , “1^(st) WERR/TOX” refers to wet etching rate of each film relative to that of standard thermal oxide film, measured for the first one minute of wet etching, while “2nd WERR/TOX” refers to wet etching rate of each film relative to that of standard thermal oxide film, measured for the second one minute of wet etching. As shown in FIG. 6 , at a high deposition temperature (650° C.), when a deposition pressure was 3,000 Pa in UHT-9, as compared with in UHT-6, -7, and -8 (400 Pa), the film deposition was highly abnormal, and no film quality was evaluated. Further, when a deposition pressure was 1,000 Pa in UHT-8, as compared with in UHT-6 and -7 (400 Pa), film quality was worsened, although it was within normal deposition. Further, as shown in FIG. 6 , the oxygen concentration of 5% to 70% was a workable range for providing adequate film quality.

It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention. 

We/i claim:
 1. A method of depositing a silicon oxide film using bis(diethylamino)silane (BDEAS) on a substrate in a reaction space by plasma-enhanced atomic layer deposition (PEALD), each repeating deposition cycle of PEALD comprising steps of: (i) adsorbing BDEAS on the substrate; (ii) purging the reaction space; (iii) exposing the substrate on which BDEAS is adsorbed to an oxidizer gas in an atmosphere in the reaction space, and applying an RF power, thereby depositing a monolayer or sublayer of silicon oxide, wherein the atmosphere has an oxygen concentration of 5% to 70% by volume in a carrier gas; and (iv) purging the reaction space; wherein the oxidizer gas is fed to the reaction space continuously throughout the deposition cycle, and wherein a pressure within the reaction space is less than 1000 Pa.
 2. The method according to claim 1, wherein the atmosphere has a pressure of 400 Pa or less.
 3. The method according to claim 1, wherein the temperature of the susceptor is not higher than 650° C.
 4. The method according to claim 1, wherein the atmosphere has an oxygen concentration of 30% to 60% by volume.
 5. The method according to claim 1, wherein one or more of the (ii) purging the reaction space and the (iv) purging is conducted for less than 2.0 seconds.
 6. The method according to claim 1, wherein the substrate has a patterned step on which BDEAS is adsorbed in step (i).
 7. The method according to claim 6, wherein the patterned step is a trench having an aspect ratio of 3 or higher.
 8. The method according to claim 1, wherein the oxidizer gas comprises nitrogen dioxide.
 9. The method according to claim 1, wherein in step (ii), oxidizer gas is fed to the reaction space at a flow rate of between 1600 and 4000 sccm, and an inert gas is fed to the reaction space at a flow rate of between 2000 and 4400 sccm.
 10. The method according to claim 1, wherein the substrate comprises a trench, and wherein the silicon oxide film is deposited on the sidewalls and the bottom surface of the trench.
 11. The method of claim 1, wherein the carrier gas is fed to the reaction space continuously throughout the deposition cycle, and wherein in step (i), the BDEAS is provided to the reaction space in a pulse by flowing the carrier gas through a bottle carrying the BDEAS.
 12. The method of claim 1, wherein the oxygen concentration is 50% to 70% by volume.
 13. The method of claim 1, wherein the oxidizer gas consists essentially of oxygen and the carrier gas.
 14. The method of claim 13, wherein the carrier gas is a noble gas.
 15. The method according to claim 1, wherein the temperature of the susceptor is greater than 400° C. 